One thing I love about my job is that I'm learning new things about the law all the time. In a recent case I was involved in I encountered the question of how can an injured person can prove that a defective product caused their injuries, when the product itself is destroyed in the event, and therefore not available to examine. In my client's case, the product was a firework that was alleged to have malfunctioned either because of a manufacturing defect, or because of misuse by the person setting it off. 

The answer is that courts have allowed defects in products to be proved by using a favorite (at least to lawyers) legal doctrine with a fancy-sounding Latin name. Washington courts have allowed proof that a manufacturing defect caused a plaintiff's injury in cases where destruction or loss of the offending product limited direct proof of the existence of a defect.  Courts have allowed the use of circumstantial evidence to prove a product manufacturing defect, and the legal mechanism for doing so is to allow proof of defect to be established in a manner similar to the way the res ipsa loquitur doctrine is used in traditional negligence cases.  See, e.g., Potter v. Van Waters & Rogers, Inc., 19 Wn. App. 746, 752-53, 578 P.2d 859 (Div. 1, 1978).

The res ipsa loquitur doctrine holds that a factfinder can, but is not required to, infer negligence on the part of a defendant if the occurrence producing the injury is of the kind that does not ordinarily happen in the absence of someone's negligence, was caused by an agent or instrumentality within the exclusive control of the defendant, and the occurrence was not due solely to the voluntary act or omission of the plaintiff. 

In Potter, 19 Wn. App. at 752-53, the court ruled that sufficient circumstantial evidence existed on the plaintiff's manufacturing defect claim to defeat a rope manufacturer's motion for summary judgment where: the rope that ended up breaking was cut from a brand new coil that recently came from the manufacturer; appeared new; had only been used once; yet broke the next day while being used in a normal fashion, resulting in the plaintiff's injury.   

The court in Potter noted that the type of circumstantial evidence which is embraced by the doctrine of res ipsa loquitur (evidence that allows the argument by a plaintiff that the failure of the product, the breaking of the rope in that case, “speaks for itself”) was permissible and would defeat a defendant's summary judgment motion.  Id. at 753.  “The accident itself, together with its attendant circumstances, affords reasonable evidence that it arose from want of proper care on defendant's part.”  Id.  See also Bombardi v. Pochel's Appliance & TV Co., 9 Wn. App. 797, 802, 515 P.2d 540 (Div. 2, 1973) (where a television was completely destroyed by self-combusting, proof of the defective condition of the product could be by direct or circumstantial evidence, and a verdict does not rest on speculation or conjecture when “founded on reasonable inferences drawn from circumstantial facts.”).